Amp Philosophy


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AMP is time tested implant
Proximal fixation is crucial
Impection bone grafting
No osteolysis

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Amp Philosophy

  1. 1. Austin Moore’s Prosthesis It’s Relevance Today Vinod Naneria Vi d N i Gi i h Y tik Girish Yeotikar A j W dh Arjun Wadhwani i Consultants Department Of Orthopaedics Choithram Hospital & Research Centre, Indore, India
  2. 2. Why AMP – Disput ? • Improper technique • Design of Implant g p • Design of instruments • No long term data from Indian scene • THR – dominated • Failures / revisions – THR – Rethinking ?
  3. 3. Question? • All successful long standing AMP develop hypertrophy of the bone all around. • Osteolysis seen early in failed AMP within months. • All successful l f l long standing THR d t di develop l some osteolysis of the bone. • Osteolysis in THR seen late and damge becomes a problem
  4. 4. Answer • Mechanical loading altering the mechanostat of bone after implant surgery decides the future of surgery surgery. • Proximal fixation at or above the level of lesser trochanter save the “disuse disuse cancellization of cortical bone” in the calcar region region.
  5. 5. The philosophy • Proximal fixation of the implant is crucial in the success of the surgery. • A tight fixation gives mechanical stability stability, and allow the grafts in the fenestration to consolidate, consolidate making it a self locking self-locking device. • Thi prevents over-loading of calcar – no This t l di fl subsidence, no loosening, no failure.
  6. 6. Mechanostat • Frost HM Strain and other mechanical HM. influences on bone strength and maintenance. maintenance Curr Opin Orthop Orthop. 1997;8:60–70. ----------------------------------------------------------- • Bone loading - Bone strength • Bone modeling – hypertrophy / normal • Bone remodeling – hypotrophy / atrophy g yp py py -----------------------------------------------------------
  7. 7. Bone modeling by drifts (A) An infant’s long bone with its original size and shape shown i solid li dh h in lid line. T k To keep it shape its h as it grows in length and diameter, modeling drifts d ift move it surfaces in tissue space as th its f i ti the dashed lines suggest. Formation drifts make and control new osteoblasts t build some d tl t bl t to b ild surfaces. Resorption drifts make and control new osteoclasts to remove bone from other t l tt b f th surfaces.
  8. 8. A different drift pattern can correct the fracture (B) malunion in a child The cross-sectional view to the right child. cross sectional shows the endocortical as well as the periosteal drifts that do the correction. (C) How the drifts in B would move the whole segment to the reader’s right. Changing the anatomy in that way reader s right reduces the bone’s bending moments; it does not eliminate bending but it does limit it Drifts are created bending, it. when and where they are needed, and they include capillaries, precursor and supporting cells, and some wandering cells. They are multicellular entities in the same sense as renal nephrons, and they usually act to minimize peak b ii i k bone strains ti
  9. 9. BMU – Renal Nephron Bone remodeling BMUs. Top row: an activation event on a bone surface at (A) makes a packet of bone resorption begin (B), (B) and then its osteoclasts are replaced by osteoblasts at (C) (C). The BMU makes and controls the new osteoclasts and osteoblasts that do this. Second row: this emphasizes the amounts of bone resorbed (E) and formed (F) by completed BMUs. Third row: in these ‘‘BMU graphs’’ (G) shows a small excess of formation over resorption. ( ) Equalized resorption and p (H) q p formation as on haversian surfaces and in ‘‘conservation-mode’’ remodeling.
  10. 10. BMU – Renal Nephron (I) A net deficit of formation, as in disuse-mode remodeling of endocortical and trabecular bone. Bottom row: these ‘‘stair graphs’’ show the effects of a series of BMUs of the kind immediately above on the local bone ‘‘bank.’’ BMUs are created when and where they are bank. needed and include a capillary, precursor and supporting cells, and some wandering cells. They are multicellular entities in the same sense as renal.
  11. 11. Strain in Cemented stems • Adaptive changes in the femur after implantation of an Austin Moore prosthesis SB Murphy, PS Walker and AL Schiller J Bone Joint Surg Am. 1984;66:437- 443. • The calcar and proximal regions are understrained because much of the loads and moments are transferred to the bone f around the distal half of the stem.
  12. 12. Un-cemented stems Un cemented • The broad proximal collar provides good resistance to axial force, whereas the distal half of the stem may carry little axial load. The varus moment on the stem is counteracted by forces at the medial part of the calcar and the distal tip, in a more concentrated manner than in a t td th i cemented stem. The radiographic appearance around uncemented stems suggests bone hypertrophy in the whole proximal area, especially medially, and local thickening at a p y y, g point level with the tip of the prosthetic stem.
  13. 13. More than 1 300 Austin Moore 1,300 hemiarthroplasties have been reviewed in the literature, literature with no reports of fracture of the stem. Results from our finite-element analysis indicate that with good calcar collar support that, calcar-collar support, the stresses in the stem are small because the stem portion of the prosthesis and the bone are uncoupled and, consequently, do not share the resultant bending moment of the head and abductor forces.
  14. 14. Calcar – Collar Support If the stem is coupled to the bone so that the resultant bending moment is shared, high stresses in the stem are predicted; such stresses are p ; inconsistent with the complete absence of fractures of these prostheses. The results of the finite- element analysis further showed that loss of calcar- collar support with proximal fixation through the fenestrations resulted in high stresses in the stem and stress shielding of the proximal medial cortex.
  15. 15. Cl Calcar – C ll S Collar Support t The uncoupled prosthesis also may be modeled with a free-body diagram as a three-force member loaded at the head, stem tip, and in the proximal region. With this model it can be shown that the reaction force of model, the stem tip, and thus the peak bending stress in the stem, stem increases as calcar-collar support is decreased calcar collar decreased. If there is no calcar-collar support, proximal support must be provided by some combination of integration y g of bone in the fenestrations and wedging due to the lateral-medial taper of the device..
  16. 16. Stresses on Stem Stresses in the stem are largest when there is no wedging, b t hi h stresses d di but high t develop i th l in the cancellous bone in the fenestrations. When there is wedging stresses in the stem can be low but wedging, low, stresses in the supporting cancellous bone can be high; additional proximal support through the g; p pp g fenestrations substantially reduces these bone stresses
  17. 17. Stresses on Stem . Ifreduced stresses in the cancellous bone are indicative of a stable device, these mechanisms indicate that fractures of the Austin Moore prosthesis have not occurred in normally loaded hips because load was transferred primarily either through the collar or by wedging, with additional support at th ith dditi l t t the fenestrations
  18. 18. Painful AMP two primary reasons AMP- • Inadequate Proximal Fixation – Loose Prosthesis –C l Calcar absorption b ti – Subsidence of the prosthesis –LLoss of varus alignment i th canal f li t in the l • Acetabular cartilage erosion
  19. 19. Inadequate Proximal Fixation • Not under our control – Elderly – Osteoporotic – Wide canal • U d our control Under tl – Faulty operative technique – Over reaming by improper Rasp – Improper selection of Implant
  20. 20. Effect of neck resection on torsional stability of cementless total hip replacement. Whiteside LA White SE, McCarthy DS LA, SE DS. Biomechanical Research Laboratory, St. Louis, Missouri, USA. Loosening of the femoral component in total hip arthroplasty commonly results from inadequate resistance to torsional loads We evaluated 20 adult loads. human cadaver femora to determine the effect of different neck-resection levels on torsional resistance of neck resection the femoral component. All specimens were prepared for fixation with the Impact modular total hip replacement. Each femoral diaphysis was overreamed 2 mm to achieve only proximal fixation. The specimens were then divided into di id d i t groups of fi and i l t were i f five d implants inserted td with the precision press-fit technique.
  21. 21. Without distal fixation, the femoral component is highly dependent on p p gy p proximal geometry for resistance to torsional loading. Preserving the femoral neck p g provides an effective means of resistance. Maintaining the entire femoral neck most effectivelyy reduces miromotion at low loads, but maintaining the midshaft area of the femoral g neck appears to most effectively control micromotion at higher torsional loads. g Resection below the midshaft of the neck markedly decreases the torsional load- y bearing capacity of the proximal femur.
  22. 22. Primary positive calcar collar contact reduced the calcar-collar incidence of calcar resorption. Sufficient cementation of the medullary canal significantly reduced the incidence of calcar resorption, as did neutral and valgus positioning of the femoral component. Loosening of the acetabular component occurred more often in the group with calcar resorption. Middle- aged patients and men were more prone t develop d ti t d to d l resorption of the calcar. Calcar resorption may be influenced by surgical technique Alteration of the technique. operative technique is recommended, with emphasis on correct valgus or neutral p g position of the femoral component, a positive calcar-collar contact, and improved cementation
  23. 23. Proximal Fixation Tips T i k Ti & Tricks • Pre operative Pre-operative assessment of the Canal Canal. • Proper neck cut. • Avoid A id comminuting C l i ti Calcar F Femoris. i • Save at least 1cm of neck at Calcar • Insert canal finder from Piriformis Fossa • In wider canal avoid use of rasp canal, rasp.
  24. 24. Proximal Fixation Tips T i k Ti & Tricks • Select proper Implant which will fill the proximal femur without increasing comminution. comminution • Use a artery forcep in the prosthesis proximal hole ( originally for extraction) for extraction), rotation control during insertion.
  25. 25. Proximal Fixation Tips T i k Ti & Tricks • Impaction grafting: – The most important area is the medial side near calcar. Graft should be inserted when nearly half of the prosthesis has gone inside. – Fill the fenestrations of the prosthesis with bone grafts, grafts as the prosthesis advances in to the canal canal. – The color of the implant should not over-hang on the calcar. – If done properly, it should rest on the neck and will compress the grafts.
  26. 26. Intra operative error during implantation of the Intra-operative uncemented Austin Moore prosthesis is relatively common. common The error rates between junior doctors and consultants were not significantly different. Austin Moore hemiarthroplasty is a technically demanding operation; the prosthesis is difficult to implant well well. Greater selectivity should be exercised when considering this prosthesis for management of femoral neck fractures.
  27. 27. (1)Inadequate length of the neck remnant (≤12 mm)-measured from the superior margin of the lesser trochanter to the resection margin at the calcar femorale If an inadequate neck femorale. remnant was identified on postoperative radiographs, radiographs the neck length from the lesser trochanter to the level of the fracture on preoperative radiographs was also measured measured. (2) Inadequate calcar seating (>1 mm)-measured from the medial prosthetic collar to calcar A calcar. prosthesis collar seated on the medial calcar was recorded as zero zero.
  28. 28. (3) Difference in prosthetic head size compared with the contralateral normal femoral head using g circular overlays-a diameter of prosthesis up to 2 mm larger to account for articular cartilage was g g considered satisfactory. If the contralateral femoral head was not suitable for analysis (due to y ( disease or previous prosthetic replacement), the ipsilateral femoral head on p p p preoperative radiographs was used for assessment of the appropriate p pp p prosthetic head size. (4) Intra-operative periprosthetic fracture- fracture classification was conducted using the Vancouver g system.
  29. 29. 147 patients were treated with the unipolar uncemented Austin Moore prostheses over the time period: 128 (87%) had surgery performed by relatively junior doctors 14% by senior medical doctors-14% officers, 57% by training registrars, and 17% by principal house officers; 19 (13%) were performed by a consultant surgeon. 84 errors in implantation were identified in 71 patients; only 76 (52%) had no errors in implantation, implantation while 52 (35%) had one error 17 error, (12%) had 2 errors, and 2 (1.4%) had 3 errors (1 4%) errors.
  30. 30. 1: Injury. 2002 Jun;33(5):419-22. Austin Moore hemiarthroplasty: technical aspects and their effects on outcome, in patients with fractures of the neck p y p ,p of femur. Parker MJ. Sharif KM, Orthopaedic Department, Peterborough District Hospital, Peterborough PE3 6DA, UK. @ g In order to determine which technical aspects of the Austin Moore hemiarthroplasty procedure affect the outcome, we reviewed 243 patients with a non-pathological intracapsular femoral neck fracture who had, Austin Moore uncemented hemiarthroplasty The immediate post operative X rays were assessed for hemiarthroplasty. post-operative X-rays alignment of the prosthetic stem, calcar seating, length of the neck remnant, leg length discrepancy and size of the head, compared with the contralateral femur. All patients were followed-up for 1 year. Significant pain at 1 year and/or revision of the prosthesis for loosening were considered as unfavourable outcomes. Inadequate calcar seating was significantly associated with pain and revision of the prosthesis (P = 0.04 and 0.01, respectively). Length of the neck remnant was also significantly associated with these two outcomes (P = 0 05 and 0 023 0.05 0.023, respectively). Difference in head size was associated with pain, but not with loosening (P = 0.01 and 0.08, respectively). The rest of the parameters were not significantly associated with the outcome. We recommend that when inserting an Austin Moore hemiarthroplasty, particular attention must be paid to the seating of the collar of the prosthesis on the calcar and correct choice of head size.
  31. 31. Injury. 2004 Oct;35(10):1020-4. C t ca ad o og ca a a ys s a te ust Critical radiological analysis after Austin Moore hemiarthroplasty. oo e e a t op asty Yau WP, Chiu KY. Department of Orthopaedic Surgery, The University of Hong Kong, Queen Mary Hospital, No. 102, Pokfulam Road, Hong Kong, PR China. The aim of this study is to investigate the causes of prosthesis loosening in patients treated with Austin Moore hemiarthroplasty (AMA). The clinical and radiological outcomes were documented in a quantitative manner after 7 years follow-up of 144 patients. At the time of final follow-up, 52 patients had died and 48 patients were lost to follow-up, leaving a total of 44 patients for analysis. Immediate post-operative X-rays were studied for the initial alignment of prosthesis, the fit of the prosthesis and the degree of osteoporosis. X-rays on latest follow-up were studied for evidence of loosening. All patients were assessed clinically with the hip score of hospital for loosening special surgery. It was found that hip pain was significantly related to subsidence and pivoting of the prosthesis (P = 0.014 and 0.035, respectively). Significant increase in subsidence was noted if the stem of prosthesis was not fitting well within the shaft of femur (P = 0.006). When the patient was younger than 73 years old at the time of operation, there was more subsidence of the prosthesis at the final follow-up (P = 0.001). It was concluded that the fill of AMA within the shaft of femur should be greater than 70% to avoid early loosening Relatively younger loosening. patients with acute fracture of the neck of femur should be treated by methods other than cementless AMA.
  32. 32. •Injury. 2004 Oct;35(10):1020-4. Critical radiological analysis after Austin Moore hemiarthroplasty. Yau WP, Chiu KY It was concluded th t th fill of AMA within th shaft of l d d that the f ithi the h ft f femur should be greater than 70% to avoid early loosening. loosening Relatively younger patients with acute fracture of the neck of femur should be treated by methods other than cementless AMA. •Injury. 2002 Jun;33(5):419-22. Austin Moore hemiarthroplasty: technical aspects and their effects on outcome, in patients with fractures of the neck of femur. Sharif KM, Parker MJ. Sh if KM P k MJ Inadequate calcar seating was significantly associated with pain and revision of the p p prosthesis ( = 0.04 and (P 0.01, respectively). Length of the neck remnant was also significantly associated with these two outcomes (P = 0.05 and 0.023, respectively). Difference in head size was associated with pain, but not with loosening
  33. 33. J Trauma. 2001 Jul;51(1):84-7. The effect of intramedullary corticocancellous bone plug for hip hemiarthroplasty. Kligman M, Zecevic M, Roffman M. Application of a corticocancellous bone plug in uncemented hip hemiarthroplasty for treatment of femoral neck fractures p p y can decrease the incidence of early thigh pain in the first 6 months. Scand J Surg. 2002;91(4):357-60. The long-term results of Lubinus interplanta hemiarthroplasty in 228 acute femoral neck fractures. A retrospective six-year f ll ft t ti i follow-up. Isotalo K, Rantanen J, Aärimaa V, Gullichsen E. The Lubinus prosthesis has a greater CCD (caput collum (caput,collum, diaphyse) angle and a longer stem compared to Thompson and Moore implants. The need for resection of calcar cortex is also limited. These biomechanical facts may explain the good long- term results of Lubinus hemiarthroplasty.
  34. 34. Loading of the calcar leading to Neck over hang & absorption
  35. 35. Impaction Grafting Reinforcement of the Calcar Femoris After One year Day One
  36. 36. Three Point Fixation Tight Femoral Canal
  37. 37. Proximal Fixation 10 years follow up came with # Tr Tr.
  38. 38. Proximal Fixation 14 years PO Broken stem Not a Failure
  39. 39. Proximal Fixation
  40. 40. Broken Stem – Not a Failure 20 years FU y
  41. 41. Bone in the fenestration A broken stem is not a failure
  42. 42. Too Much Valgus Too Mush Varus
  43. 43. Subsidence S b id No proximal Fixation
  44. 44. Subsidence
  45. 45. Ideal Prosthesis Fitting F moderately wide canal For d l id l 1.Correct offset 2 Correct sitting over calcar 2.Correct 3. Correct Varus setting 4. Three point fixation p For Narrow canal the junction below the fenestrations is too much angulated, angulated Needs a straight stem
  46. 46. Intra-operative error during AMP hemiarthroplasty.J. hemiarthroplasty J of Ortho Surgery Weinrauch, P • 147 patients were treated with th unipolar uncemented ti t t t d ith the i l td Austin Moore prostheses over the time period: 128 ( (87%) had surgery p ) g y performed by relatively j y y junior • doctors-14% by senior medical officers, 57% by training registrars, and 17% by principal house officers; 19 (13%) were performed by a consultant surgeon surgeon. • 84 errors in implantation were identified in 71 patients; only 76 (52%) had no errors in implantation, while 52 y ( ) p , (35%) had one error, 17 (12%) had 2 errors, and • 2 (1.4%) had 3 errors.
  47. 47. Burminghum Study • G H hospital U K U.K. • 188 patients Infection 4 5% I f ti 4.5% Dislocation 3.4% Loosening 3.4% Journal of injury - 2001
  48. 48. AOSJ - 1991 June quality of life 185 patients – average 80 yrs ti t 7% dislocation 4% deep infection 1% prostr sio prostrusio 2% loosening of prosthesis 5 yrs -- > 60% mortality in both groups Half of pts & most of the controls able to move independently.
  49. 49. Peri-prosthetic fracture
  50. 50. AMP was well fixed Could not be removed Locking / Mamman’s plate Mamman s
  51. 51. “Don’t throw away the AMP Don t AMP” Says Marcus R ER.E. From University hospital of Cleveland Ohio (journal of A th l t 2002) (j l f Arthroplasty AMP Bipolar 7% died(3 months) 11% died HHS Avg 75(26 mon) 78 Avg Avg.75(26 (55 to 92) (60 to 94)
  52. 52. Particular attention must be paid to the p seating of collar of the th prosthesis on th i the calcar & correct choice of head size.
  53. 53. Method is very easy to be learnt. Cost effective, well tolerated by aged patients German article
  54. 54. 154 AMP for 10 yrs At 3yrs 46% community ambulance 10% household 35% non functional ambulance Men had better than women Harris hip H i hi score -- 69 – 55yrs 59 – 10yrs Failure rate -- > 5 yrs – 6 5% 6.5% 10 yrs – 7.7% Revision rate -- > 5 yrs - 4.5 % y 10 yrs – 5.2%
  55. 55. A case of THR done 14 Years ago Now the N th CUP showing d f h i deformation ti No complaints A.M.P. 16 years ago. Awaiting Revision?
  56. 56. Summary • In our setup AMP serves purposeful satisfactory function in elderly individuals • Average ortho surgeon can perform this surgery comfortably in average set-up. • Pl th surgery b f Plan the before h d & ask hand k for appropriate stem width according to f t femoral canal. l l
  57. 57. Summary • Carefully reaming in narrow femoral canal. • No reaming in Osteoporotic bone. bone • Use bone grafts from femoral head for calcar reinforcement • Always fill the fenestrations with bone grafts. ith b ft
  58. 58. Conclusions • AMP is time tested implant and results are satisfactory. • THR, cemented bipolar has got their own , p g indications, & they are also not free from serious complications. • AMP is Cost effective, • Bone cement can be used as last option. • Further improvement in the implant design is recommended.
  59. 59. 22 years old Male Fracture N/F AVN 1998 AMP working since then
  60. 60. THR - fail • Material failure • Friction failure • Cement di C t disease • Design failure • Particle disease • Material failure • Mechanical failure - Mechanostat
  61. 61. Proxima – Depuy a conservative metaphyseal implant py p Proximal Fixation
  62. 62. Proxima DePuy Well fixed AMP
  63. 63. AMP Still working
  64. 64. “Don’t throw away y the th AMP”
  65. 65. DISCLAIMER Information contained and transmitted by this presentation is based on personal experience and collection of cases at Choithram Hospital & Research centre, Indore, India, during last 25 years. It is intended for use only by the students of orthopaedic surgery. yy p gy Views and opinion expressed in this presentation are personal opinion. Depending upon the x-rays and clinical presentations, viewers can make their own opinion. opinion For any confusion please contact the sole author for clarification. Every body is allowed to copy or download and use the material best suited to him. I am not responsible for any controversies him arise out of this presentation. For any correction or suggestion please contact @y